This application claims the benefit of Korean Application No. 2001-31970, filed Jun. 8, 2001, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an actuator for an optical pickup, and more particularly, to an actuator for an optical pickup having an improved structure in which assembly is easier and sensitivity is increased.
2. Description of the Related Art
An actuator for an optical pickup drives an objective lens in a focusing direction, in a tracking direction and/or in a tilting direction. Actuators for optical pickups include moving coil type actuators, which have a coil installed on a bobbin, and moving magnet type actuators, which have a magnet installed on a bobbin.
Referring to FIG. 1, a conventional moving coil type actuator for an optical pickup includes a pair of focusing and/or tilting coils 11 installed at opposite ends of first sides of a bobbin 14 on which an objective lens 51 is installed. A pair of tracking coils 15 are installed at opposite ends of second sides of the bobbin 14. Tracking magnets 17, which are opposite the corresponding tracking coils 15, are installed on a base 10. Focusing and/or tilting magnets 13 are fixed and installed on external yokes 53, which are installed on the base 10 opposite the corresponding focusing and/or tilting coils 11. Internal yokes 55 are installed on the base 10 opposite the corresponding focusing and/or tilting coils 11. One end of each of four wires 19, which support the bobbin 14, and one end of each of two wires 19a, which are used to drive the bobbin 14 in a tilting direction, are coupled to the bobbin 14. The other end of each of the four wires 19 and the two wires 19a are coupled to a mount 12. The mount 12 is fixed to the base 10. The four wires 19 and the two wires 19a are paths used to apply current to the pair of focusing and/or tilting coils 11.
In the conventional moving coil type actuator for an optical pickup shown in FIG. 1, since the pair of focusing and/or tilting coils 11 and the pair of tracking coils 15 drive the objective lens 51 in focusing and tracking directions using a synchronous driving method, and the pair of focusing and/or tilting coils 11 drive the objective lens 51 in a tilting direction using an asynchronous driving method, the two wires 19a as well as the four wires 19, which are used as paths for applying current to the pair of focusing and/or tilting coils 11, are required. That is, six wires (four wires 19 and two wires 19a) are required for the conventional moving coil type actuator for an optical pickup shown in FIG. 1.
Since the bobbin 14 is light in weight, the conventional moving coil type actuator has a high sensitivity. However, since six wires (four wires 19 and two wires 19a) are required to drive the bobbin 14 in focusing, tracking, and tilting directions, the conventional moving coil type actuator has a complicated and cluttered structure and is difficult to assemble. That is, it is very difficult to attach six wires (four wires 19 and two wires 19a) to the narrow sides of the bobbin 14, resulting in an increase in defects.
Referring to FIG. 2, a conventional moving magnet type actuator for optical pickup includes four magnets 27, pairs of which are installed at corresponding opposite sides of a bobbin 24. At the center of the bobbin 24 is installed an objective lens 61. Two pairs of focusing and/or tilting coils 21 and two pairs of tracking coils 25 are installed on corresponding sides of a base 20 opposite corresponding pairs of the magnets 27. Four holders 29, which support the bobbin 24, are installed in a mount 22, which is fixed to the base 20. The four holders 29 only support the bobbin 24, and are thus unlike the wires 19, 19a of the conventional moving coil type actuator shown in FIG. 1.
As shown in FIG. 2, in the conventional moving magnet type actuator, the four magnets 27 are installed on the bobbin 24 and thus increase the mass of the bobbin 24. This increase in mass results in a decrease in a sensitivity of the actuator. Also, since the conventional moving magnet type actuator does not include yokes, it is difficult to obtain a path for a magnetic field. This difficulty decreases the efficiency of magnetic force in affecting the coils 21, 25.
To solve the above and other problems, it is an object of the present invention to provide an actuator for an optical pickup having an improved structure which is easier to assemble than a conventional moving coil type actuator for an optical pickup, and is more sensitive and uses magnetic force more efficiently than a conventional moving magnet type actuator for an optical pickup.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects, there is provided an actuator for an optical pickup according to an embodiment of the invention that includes a bobbin on which an objective lens is installed, holders coupled between a mount installed on a base and the bobbin to support the bobbin such that the bobbin is movable with respect to the base, and a magnetic circuit installed in the bobbin and in the base to drive the objective lens in focusing, tracking, and tilting directions, wherein the magnetic circuit includes coils installed on the bobbin and which drive the objective lens in one direction selected from focusing, tilting, and tracking directions, and magnets installed on the bobbin to drive the objective lens in another direction selected from the focusing, the tilting, and the tracking directions.
According to an aspect of the invention, the magnetic circuit includes first and second coils installed at opposite first sides of the bobbin and are used to drive the objective lens in the focusing and the tilting directions, first and second magnets installed on the base opposite the corresponding first and second coils, tracking magnets installed at opposite second sides of the bobbin and are used to drive the objective lens in the tracking direction, and tracking coils installed on the base opposite the corresponding tracking magnets.
According to another aspect of the invention, the magnetic circuit includes first and second magnets installed at opposite first sides of the bobbin and are used to drive the objective lens in the focusing and the tilting directions, first and second coils installed on the base opposite the corresponding first and second magnets, tracking coils installed at opposite second sides of the bobbin and are used to drive the objective lens in a tracking direction, and tracking magnets installed on the base opposite the tracking coils.
According to yet another aspect of the invention, the holders comprise wires or leaf springs and are used as paths to apply current to the tracking or first and second coils installed on the bobbin.
According to still another aspect of the invention, the actuator further includes yokes to improve the efficiency of a magnetic force of the magnetic circuit.
According to still yet another aspect of the invention, the actuator further includes internal yokes installed on the base opposite the corresponding first and second coils, or external yokes installed on the base opposite the corresponding first and second magnets installed opposite the first and second coils.
According to a further aspect of the invention, the actuator further includes internal yokes installed on the base opposite the corresponding tracking coils, or external yokes installed on the base opposite the corresponding tracking magnets installed opposite the tracking coils.
According to a yet further aspect of the invention, the first, second, and tracking coils comprise fine pattern coils (FPCs).
According to a still further aspect of the invention, the actuator includes less than 6 wires connected to the bobbin.
According to a still yet further aspect of the invention, fewer than 4 magnets are on the bobbin having the fewer than 6 wires.